nginx: security bump to version 1.8.1

Fixes:

CVE-2016-0742 - invalid pointer dereference might occur during DNS
server response processing if the "resolver" directive was used,
allowing anattacker who is able to forge UDP packets from the DNS server
to cause segmentation fault in a worker process.

CVE-2016-0746 - use-after-free condition might occur during CNAME
response processing if the "resolver" directive was used, allowing an
attacker who is able to trigger name resolution to cause segmentation
fault in a worker process, or might have potential other impact.

CVE-2016-0747 - CNAME resolution was insufficiently limited if the
"resolver" directive was used, allowing an attacker who is able to
trigger arbitrary name resolution to cause excessive resource
consumption in worker processes.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>